Mr Obama, speaking at a retirement ceremony honoring Admiral Mike Mullen, reiterated his commitment to destroy terrorist networks, saying "we will remain vigilant against any threats to the United States or our allies."

"This is further proof that al-Qaeda and its affiliates will have no safe haven anywhere in the world," Obama said. He is the most prominent al-Qaeda figure to be killed since bin Laden's death in May.

Mr Obama added that al-Awlaki's death was a result of the government of Yemenjoining international efforts against the militants.

Awlaki, identified by US intelligence as "chief of external operations" for al-Qaeda in the Arabian Peninsula, was killed in a CIA drone attack in a remote Yemeni town, US officials said.